Remove the shells from the pistachios and place them in a food processor. Process until you have small pieces, it's not necessary to have it super fine. Reserve.
Beat the butter with the sugar, salt and oil until the mix becomes lighter in colour. You can do this with an electric mixer or using a hand-held whisk.
Add the eggs and beat them again until they are fully incorporated and the mix looks airy. From all the beating, the mix should thicken and start to unstick from the sides of the bowl.
Add the milk and vanilla extract and mix. It will look split, but don't worry. It will come back with the flour.
Add the flour, pistachios and baking powder and mix.
Grease your bundt pan with melted butter. You can paint it onto the pan or use a piece of kitchen paper to spread it around. Flour the pan. After distributing the flour around the inside of the pan, turn it upside down and pat it to remove the excess.
Place the batter inside the pan and spread it out.
Bake the cake at 180°C/350°F for 45min-1hour or until when you insert a knife, it comes out clean. It's important to not overcook it to prevent it from drying out. If you have an electric oven, check the cake at the 30-minute mark. If it's golden enough on top, change the heat source to only the bottom.
While it's still hot, turn the pan over onto a cooling rack. Lift the pan off the cake carefully, and allow it to cool completely.
Once at room temperature, dust with icing sugar.